There are 2 major versions of WinDVD, just like with WinDVD 3.0, a standard version and a Plus version that has all the extras such as Dolby Pro Logic II, Dolby EX, DTS ES matrix support, and some additional gamma/color adjustments.
New Audio Features
WinDVD 3.0 was first to introduce DTS decoding, and WinDVD 4 Plus retains this quite useful feature. PowerDVD 4.0 also introduced Dolby EX and DTS ES, as well as Dolby Pro Logic II support, and so it is no surprise that WinDVD 4 Plus also features support for all of these audio formats.
2/4/5.1/6.1 and even 7.1 audio is now supported, for those lucky enough to have the required soundcard and all those speakers.
Dolby Pro-Logic II decoding has been added, which allows you to enjoy multi-channel audio from a standard 2-channel track.
The reverse is also true in that the new SRS TruSurround XT support means that multi-channel audio tracks can be outputed through 2 speakers, and the surround sound "simulated" by using audio effects (by tricking your brain into thinking the sound is coming from all sides - similar to what Dolby Headphone does with stereo headphones). There is also SRS "Dialog Clarity" and "TruBass", which improves the diaglog clarity, and increases overall bass. There is even a "speaker size" option, which allows you to set how powerful your speakers are and how much bass WinDVD should send to them (otherwise, it will probably go to your subwoofer, if you have one).
Last, but not least, there are a whole range of Audio Effects like ones normally found on home theatre receivers, such as "Hall", "Soft", "Echo" ... there are also environmental effects such as "Theatre" and "Late Night". There are also karaoke settings, such as pitch control, found on many karaoke enabled standalone DVD players.
New Video Features
WinDVD's video decoder is known to be the best quality, so any improvement here would be a bonus. I could not find any changes from the previous version, which is not a bad thing considering the previous version has very good video quality.
What is new, however, is the host of brightness/contrast/color adjustments, which has been simplified somewhat from previous versions. The Plus version of WinDVD also has GAMMA correction.
The video capturing functions in previous version of WinDVD was a major dissapointment, but WinDVD has done the exact opposite here and made video capture one of the highlights of this new version. There is now a dedicated "Capturing Browser", which allows you to capture multiple frames and preview/delete/save them here with ease.
There is also a similar "Bookmark Browser", which allows you to bookmark certain scenes and come back to them at later time.
New Playback Modes
Following PowerDVD 4's lead in bringing ripped DVD playback support (play ripped DVDs off your hard-drive), WinDVD 4 has added the same function in its "DVD From Folder" function.
There is also a new mode called "PAL TruSpeed", which as the name suggests, plays back PAL DVDs at their true speed, rather than the slightly off speed in most software DVD players. The actual difference is quite small, so most of you would not have noticed it if I didn't mention it.
Last, but not least, is the new "Video Window" options, which includes the much needed "Always On Top" feature, and the new "Video Desktop" feature. "Video Desktop" actually allows you to playback the DVD as the background image of your Windows desktop.
New Interface Features
The skin has been changed for WinDVD 4, although this appears to be done due to functional changes, rather than just a cosmetic change.
Subpanels have been introduced to control the most frequently accessed functions. The system setup/configuration section has also been changed, but most other features remain similar to the previous version.
All Windows versions, except for Windows 95, are supported by this WinDVD version.